Brazing sheets are conventionally used as material for heat exchangers of automobiles and the like. A brazing sheet is formed of an aluminum alloy (hereinafter sometimes referred to as an “Al alloy”) including a core layer and either a brazing filler layer or a sacrificial layer formed on both sides of the core layer.
In recent years, automobile heat exchangers have tended to reduce their weight and size. With such reductions, the brazing sheets for forming tubes, which occupy the majority of the mass of the heat exchanger, have been required to be thinned. The brazing sheet is thinned to about 200 μm so far; however, to make the brazing sheet much thinner, it needs to have higher strength and corrosion resistance corresponding to the further thinning. However, if the thickness of the core layer is reduced for the thinning of the brazing sheet, the brazing sheet will have difficulty in ensuring the post-brazing strength. On the other hand, if the thickness of the sacrificial layer is reduced, the corrosion resistance becomes difficult to ensure. Further, if the thickness of the brazing filler layer is reduced, the brazability will be degraded.
To address these issues, many studies have been conventionally done. For example, Patent Document 1 discloses a brazing sheet with excellent brazability and post-brazing strength that utilizes an Al—Si—Fe—Cu—Mn—Mg based alloy as the core layer of the brazing sheet. Patent Document 2 discloses a clad material that exhibits excellent post-brazing strength, corrosion resistance and brazability by using an Al—Si—Mn—Cu—Ti based alloy as the core layer of the brazing sheet.